The present invention generally relates to compressor systems and, more particularly, to oil flooded, rotary screw gas compressor systems having lube-oil circulation systems and apparatus. The present invention relates to a method for enhancing the production from those systems by utilizing a reliable, non-disposable coalescing system to enlarge and entrain liquid particles in a multi-step process yielding a cleaner, liquid free stream than currently available methods.
Helical lobe rotary compressors, or "screw compressors," are well-known in the air compressor refrigeration and natural gas processing industries. This type of gas compressor generally includes two cylindrical rotors mounted on separate shafts inside a hollow, double-barreled casing. The side walls of the compressor casing typically form two parallel, overlapping cylinders which house the rotors side-by-side, with their shafts parallel to the ground. As the name implies, screw compressor rotors have helically extending lobes and grooves on their outer surfaces. During operation, the lobes on one rotor mesh with the corresponding grooves on the other rotor to form a series of chevron-shaped gaps between the rotors. These gaps form a continuous compression chamber that communicates with the compressor inlet opening, or "port," at one end of the casing and continuously reduces in volume as the rotors turn and compress the gas toward a discharge port at the opposite end of the casing. The compressor inlet is sometimes also referred to as the "suction" or "low pressure side" while the discharge is referred to as the "outlet" or "high pressure side."
Screw compressor rotors intermesh with one another and rotate in opposite directions in synchronization within a housing. The impellers operate to sweep a gas through the housing from an intake manifold at one end of the housing to an output manifold at the other end of the housing. Commercially available compressors most commonly include impellers or rotors having four lobes, however, others have been designed to have five or more lobes, however, it may be possible to use a rotor or impeller which has only 2-5 lobes. The present invention relates to a system used in conjunction with this type of rotors.
The rotor shafts are typically supported at the end walls of the casing by lubricated bearings and/or seals that receive a constant supply of lubricant from a lubricant circulation system. Since the lubricant is typically some type of oil-based liquid compound, this part of the compressor system is often referred to simply as the "lube-oil" system. However, the terms "lubricant," "lube-oil," and "oil" encompass a wide variety of other compounds that may contain other materials besides oil, such as water, refrigerant, corrosion inhibitor, silicon, Teflon.RTM., and others. In fact, the name "lube-oil" helps to distinguish this part of the compressor system from other components that may use similar types of oil-based fluids for other purposes, such as for power transmission in the hydraulic system or insulation in the electrical system.
Like the lube-oil circulation system in many automobiles, compressor lube-oil systems generally include a collection reservoir, motor-driven pump, filter, and pressure and/or temperature sensors. Since many lubricants degrade at high temperature by losing "viscosity," lube-oil systems for high temperature applications, such as screw compressors, generally also include a cooler for reducing the temperature of the lubricant before it is recirculated to the seals and bearings. So-called "oil flooded" rotary screw compressors further include means for recirculating lubricant through the inside of the compressor casing. Such "lube-oil injection" directly into the gas stream has been found to help cool and lubricate the rotors, block gas leakage paths between or around the rotors, inhibit corrosion, and minimize the level of noise produced by screw compressors.
A typical oil flooded screw compressor discharges a high-pressure and high-temperature stream consisting of a mixture of gas and oil. The oil and any related liquid must be separated from the high pressure gas. The present invention relates to a technique for coalescing the liquid and oil particles by multi-step process, wherein the first step entrains the particles using a first vane pack and a flow at high velocity, and then a second step passes the particles and gas through a second vane pack, thereby removing essentially all of the liquid and oil particles, creating an essentially liquid and oil free gas stream.
At least two, but optionally, a plurality of vane packs can be used in sequence in the present invention to achieve the desired clean stream effect. The vane packs, which are the coalescing means or "coalescer means", are connected to each other in series and connected based on a defined size relation. In particular, the first vane pack is smaller in surface area than the second vane pack. After leaving the vane packs, which are also called chevron shaped mist eliminators, the gas stream is cooled, filtered, and recirculated to the compressor bearings and main oil injection port.
There are a variety of patents which generally relate to screw compressors and compressors in general, such as U.S. Pat. Nos. 5,439,358, 2,489,997 and 3,351,227 but none discloses the multi-pack filtering concept using vane packs as described in the present invention. Related patents which discuss compressor features, but not the multi-vane pack system of the invention include U.S. Pat. Nos. 5,564,910, 5,490,771, 5,405,253, 4,758,138, 5,374,172, 4,553,906, 5,090,879, 4,708,598, and 5,503,540.